This invention relates to sequentially deposited inhomogeneous magnetooptical recording media having novel properties.
Desirable magnetooptical films are those which are eraseable and on which signals can be written at high density with small light-thermal energy at good writing and read-out efficiency. In such films, the signal of the recording medium is proportional to the polar Kerr rotation angle while the sensitivity of the medium depends its the coercitivy.
One of the difficulties involved in producing such films resides in the fact that the Kerr rotation angle and the coercive force change independently for any given alloy so that a composition having a large Kerr rotation angle does not always have the desired coercitivy. Several investigators have reported on the relationship between the Kerr rotation angle and the composition of alloy films. Tsujimoto et al (Magnetic and magneto-optic properties of amorphous TbFeCo magnetic films, IEEE Transactions on Magnetics, Vol. Mag-19, No 5, September 1983, pp. 1757-1759) and U.S. Pat. No. 4,670,353 teach that a high angle of Kerr rotation can be obtained when Co is substituted for a portion of the Fe in amorphous TbFe magnetooptical films.
It has been found, however, that the method used to prepare a film and the control of specific parameters can critically influence both the Kerr rotation angle and coercivity to provide magnetooptical media having novel properties even when produced from TbFeCo alloy compositions.